Heavy off-road vehicles or trucks which are designed to carry heavy loads of cargo typically include a wheeled frame and a truck body portion supported by the frame. The truck body portion of such vehicles can carry loads in the range of 35 to 300 tons. Out of necessity, such vehicles employ some sort of shock absorbing device as part of the suspension system.
During operation, such vehicles operate in either of two conditions: empty or loaded. In these applications, the difference in weight or load acting on the vehicle suspension system can be quite substantial and a single element suspension system will perform poorly in one or the other condition. In the 1990's there was a change in the industry regarding suspension design. The OEM's all perceived a need and desire for better ride quality with an emphasis on when the vehicle was operating in an empty condition. It is most desirable to the vehicle driver to have a suspension system which offers a relatively soft ride when the load is at a minimum but yet is stiffer when the supported load is at a maximum whereby improving load stability.
Moreover, the OEM's of such vehicles desired the ability to monitor and record the actual loads being carried in the truck body portion of each vehicle. As such, it would be possible to optimize the amount of loading of the vehicle and thereby increase component life, maximize productivity and monitor vehicle activities, i.e., rough road conditions, and the like.
Thus, there is a continuing need and desire for a dual rate shock absorbing apparatus for a suspension system of a heavy off-road vehicle which works in a first or relatively soft condition when the supported load is at a minimum and a second relatively stiff condition when the supported load being carried by the vehicle is significantly greater. Moreover, there is a continuing need and desire for such a dual rate shock absorbing apparatus for a off-road heavy duty vehicle suspension system which has the ability to monitor and provide an indication of the loads acting on the suspension system.